Daytime Fireball, Sonic Boom Surprises Calif., Nevada Spectators

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Residents in California and Nevada reported hearing a sonic boom
and seeing a bright fireball streak across the sky early Sunday
morning (April 22), according to news reports.

Experts said the sonic boom and fireball
were likely caused by a meteor passing through Earth's
atmosphere. The explosive noise shook some homes and startled
unsuspecting people across both states, reported the Associated
Press.

Calls were placed to local law enforcement agencies after the
event, and several eyewitnesses initially thought they had
experienced an earthquake.

"It made the shades in my room shake hard enough to slam into the
window a couple times," Nicole Carlsen, who lives in the Reno
area,
told the AP. "I kept looking for earthquake information, but
(there was) nothing. I even checked the front of my house to make
sure no one ran into the garage. I wish I had seen the meteor."

Bill Cooke, head of NASA's Meteoroid
Environments Office at the Marshall Space Flight Center in
Huntsville, Ala., is currently analyzing data on the fireball,
and made early estimates on the size of the space rock.

"The fact that sonic booms were heard indicates that this meteor
penetrated very low in [the] atmosphere, which implies a speed
less than 15 km/s (33,500 mph)," Cooke told SPACE.com in an
email. "Assuming this value for speed, I get a mass for the
meteor of around 70 metric tons. Hazarding a further guess at the
density of 3 grams per cubic centimeter (solid rock), I calculate
a size of about 3-4 meters, or about the size of a minivan
(though much, much more massive)." [ Fallen
Stars: Famous Meteorite Photos ]

Cooke called Sunday's fireball a "big event," based on the amount
of energy that was released as the meteor entered the atmosphere.

"The energy is estimated at a whopping 3.8 kilotons of TNT (about
one fourth the energy of the "Little Boy" bomb dropped on
Hiroshima), so this was a BIG event," he explained. Cooke added
that this does not mean that there was a 3.8 kiloton explosion on
the ground in California; instead, " the meteor possessed this
amount of energy before it broke apart in the atmosphere above
that state."

When would-be meteors are traveling through space, they are known
as meteoroids to astronomers. When they enter Earth's atmosphere
to create fireballs, they are called meteors. Only fragments that
actually reach Earth's surface are called
meteorites.

Sunday's sonic boom was so powerful it rattled houses in
California and Nevada, according to news reports.

"It knocked me off my feet and was shaking the house," Erin
Girard-Hudson of Arnold, Calif., told The Union Democrat of
Sonora, Calif., according to the AP. "It sounded like it was next
door."

"[W]ithout a trajectory, I cannot rule out a Lyrid origin, but I
think it likely that it was a background or sporadic meteor," he
said.

Greg Giroux of June Lake, Calif., witnessed the fireball from the
eastern Sierra, just west of Yosemite National Park. He said the
rare daytime fireball created a spectacular light show as it
passed overhead.

"This was by far the brightest fireball/shooting star I've ever
seen, especially since it was in full sunlight," Giroux told the
AP. "After the flash, it broke up into pieces, then I lost sight
of it as it went behind a mountain."

Editor's Note: If you snapped a photo of the fireball and would
like to share it with SPACE.com for a possible story or gallery,
please contact managing editor Tariq Malik at tmalik@space.com.

You can follow SPACE.com staff writer Denise Chow on
Twitter@denisechow.
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